microphotometer vs densitometer

microphotometer and densitometer both are nouns.

Word	Noun	Adjective	Verb	Adverb
microphotometer	Yes	No	No	No
densitometer	Yes	No	No	No

As nouns, densitometer is a hypernym of microphotometer; that is, densitometer is a word with a broader meaning than microphotometer:

microphotometer: special kind of densitometer that measures density variations over a very small area
densitometer: a measuring instrument for determining optical or photographic density

microphotometer (noun)	densitometer (noun)
special kind of densitometer that measures density variations over a very small area	a measuring instrument for determining optical or photographic density
	a measuring instrument for determining density or specific gravity